<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>

  <style>
    div{
      color: red;
      font-size:18px
    }
  </style>
</head>
<body>
  <div >我是一个div</div>
</body>
</html>